One of the most demanding applications for building materials is use in foundation or basement walls. Such walls structures are subject to the weight of the building (weight tangential to the surface of the wall, or shear forces), as well as the weight of the surrounding ground, which exerts forces normal to the wall or wall panels. Besides the structural demands, such walls and the materials constituting them must be reasonably water-resistant, and preferably have a reasonably high insulating value (R value).
Standard residential and light commercial foundations are made of concrete-based products in a variety of different forms and embodiments. One embodiment is manufactured on the building site in the form of poured concrete. Another popular variation is pre-shaped and furnace-fired blocks (commonly called cinder blocks), which are manufactured at a factory and sent to a building site to be assembled using mortar and other well-known techniques. Foundation walls of this nature have been used since ancient times. These types of structures have had wide acceptance, and have enjoyed apparent success in a number of variations and embodiments. Some examples are described below.
One variation of a foundation wall is found in U.S. Pat. No. 4,856,939 to Hilfiker, issued Aug. 15, 1989 and incorporated herein by reference. In this patent, a retaining wall, to withstand a mass of earth, relies on polymer geogrids for reinforcement and wire trays to provide a solid face against the adjacent earth, which is to be held in place. The wire trays are L-shaped with intersecting floor and face sections. Hooked extensions formed on the face sections serve to secure the trays in a superimposed relationship to hold the geogrids in place against the trays. The geogrids extend distally from the trays to provide deep reinforcement. While the necessary structural strength is obtained to form a proper retaining wall, the techniques and materials are not appropriate for a foundation wall, as used in a dwelling, also the retaining wall of Hilfiker, cannot maintain the integrity of a structure or building resting on that wall. Nor is the retaining wall of Hilfiker appropriate for preventing the migration of moisture, or maintaining a reasonable R factor.
The structural integrity to withstand the normal stresses incurring for a foundation wall or retaining wall is provided by open-mesh structural textiles in U.S. Pat. No. 6,056,479 to Stevenson, et al., incorporated herein by reference. A structural textile is formed from at least two and preferably three components. The first component or load-bearing member is a high tenacity, high modulus, and low elongation yarn. The yarn can be either monofilament or multifilament. The second component is a polymer in the form of a yarn or other form, which will encapsulate and bond yarn at the junctions to strengthen the junctions. The third component is an optional effect or bulking yarn. In the woven structural textile, a plurality of warp yarns are woven with a plurality of weft (filling) yarns. The weave is preferably a half-crossed or full-crossed leno weave. The high structural integrity is provided in a wide variety of different shapes and applications and can withstand high normal stresses. However, open mesh structural textile is not suitable as a foundation wall material since substantial support for the structural textile is still required. Further, there is no moisture integrity or R factor provided by the structural textile.
Overall structural integrity apparently appropriate for a foundation wall is provided by the system of U.S. Pat. No. 6,041,561 to LeBlang, issued Mar. 28, 2000, and incorporated herein by reference. This system relies upon pre-fabricated, self-contained building panels, including a panel incorporating a truss structure as a part thereof. The panels include a skeletal assembly generally comprising an array of structural steel channels, rigid sheeting arranged proximate to the channels, and support members adjacent the rigid sheeting. The channels are supported between suitable base plates. The structure further includes angles for defining portions of the skeletal assembly and a forming structure, which is used as part of the skeletal assembly. The skeletal assembly and forming structure are oriented horizontally on a plane or surface. A self-hardening material, such as concrete, clay, or the like, is introduced to the forming structure for the embedding at least a portion of the skeletal assembly. The forming structure becomes an intrical part of the completed building panel, and is not removed therefrom. A building truss, including a pair of double-angle struts and a web-reinforcement bar threaded therealong, and rigid sheeting are arranged to define a receiving chamber for the self-hardening material.
The self-contained building panels can be made entirely at a factory for shipment in large segments to building sites, or the panels can be formed by pouring the concrete into the appropriate portions of the panels at the building site. It should be noted that large wall segments that are formed entirely at the factory are problematical due to the weight of the concrete. Using an alternative method of pouring the concrete at the building site introduces problems of quality control and uniformity. Further, the LeBlang system appears to be entirely subjected to the limitations imposed by the characteristics of concrete.
There are a number of limitations to poured concrete or cinder block foundation walls. Despite its strength in compression, cinder block and even poured concrete walls fail due to constantly changing load factors brought on from drastic temperature changes (in conjunction with water migration into the wall material), water-saturated soil, soil shifting, and shock waves from external disruptions transmitted through the ground to the foundation wall. One source of shock waves is earthquakes. Other examples would include explosive forces (both deliberate and accidental), as well as massive shifts in nearby ground structure due to clumsy construction techniques. Soil is essentially a slow-moving fluid, which is always shifting. As a result, there are constantly changing forces working on any foundation wall.
Concrete and cinder block walls that are inundated by water are seldom able to resist the penetration of moisture. Moisture migration introduces the possibility of toxic mold occurring in residential buildings. This becomes a critical factor in obtaining insurance coverage, which is often denied for residential structures having moldy interiors Further, if the water remains standing around the wall, and freezes, structural failure certainly occurs. As a further complication, concrete has uneven drying characteristics. This results in varying strengths throughout a poured concrete wall.
The molecular consistency of concrete is coarse. As a result, concrete has very little insulating value. Further, concrete absorbs, retains and wicks water to the interior of the structure that includes the foundation wall. This tendency is even more pronounced with cinder block. Just as moisture vapor can penetrate a concrete wall, so does Radon gas. This is particularly problematical in certain areas of Radon occurrence. A sufficient number of high Radon areas exist so that Radon has become the second leading cause of cancer in the United States. This factor becomes particularly critical in basements used as exercise rooms since heavy breathing increases the likelihood of Radon intake.
Poured concrete for building foundation walls is expensive, complicated, and time-consuming. Less expensive alternatives, such as cinder blocks, are widespread. However, the use of cinder block has its limitations. For example, skilled masons are necessary to erect any structure using cinder block, and additional treatment of the wall (such as filling the holes in the blocks) are often necessary to provide minimum standards of insulation, structural strength, and resistance to moisture migration. Further, because mortar is used throughout a cinder block wall, the wall loses flexibility that might have been provided by the use of multiple pieces as opposed to solid slab of concrete.
Both types of foundation wall fracture under a variety of loads that may introduce tensile stress at various points along the wall. Further, the fact that poured concrete foundations and cinder block foundation walls are fabricated at the building site by individuals of varying degrees of skill results in non-uniformity of structure, and higher rates of failure than would result from uniformly manufactured building panels subject to the quality control standards of a factory.
Another drawback of concrete foundation walls is its very low insulation capability or R factor, usually in the range of 1.4 to 3.0. Consequently, additional insulation must be added to foundation walls. This is expensive, complex, and time-consuming.
Even more detrimental is the damage to wooden structures supported by such foundation walls. The passage of moisture through concrete foundation walls dissipates through the rest of the structure, degrading wooden structural parts. The moisture can attack conventional structures in a number of ways, including: expansion damage in buildings in locations, which are subject to freezing temperatures; opening paths for insects; introducing mold problems; increasing the possibility of Radon gas occurrence; and, degrading thermal insulation.
As a result of some of the aforementioned problems, many modern wooden structures have severely limited usable lifetimes. Accordingly, framed structures on concrete or cinder block foundations have to be replaced relatively frequently.
A superior foundation wall system would eliminate all of the aforementioned disadvantages of conventional foundation wall systems, and would extend the lifetimes of the structures placed on those foundation walls. A desirable, improved foundation wall system would provide far greater tensile strength (and thus overall strength) than conventional poured concrete or cinder block walls, as well as providing a good R factor and impermeability to moisture. Preferably, the improved foundation wall system would have a much greater capability to withstand earthquake forces than conventional foundation wall systems.